1. Field of the Invention
The present invention relates to a technology of monitoring plasma in a chamber of a plasma processing apparatus and so on; and more particularly, to plasma monitoring method and apparatus for measuring electron density in plasma and light emission from the plasma.
2. Description of the Related Art
In etching, depositing, oxidizing and sputtering treatments of a semiconductor device or flat panel display (FPD) manufacturing process, plasma is widely used to cause processing gas to desirably react at relatively low temperatures. Generally, in a plasma processing apparatus, it is necessary to uniformly perform plasma treatment over a surface of a substrate to be processed so as to obtain a high yield. To this end, it is necessary to create plasma so that plasma density, i.e., electron density, is uniformly distributed in a processing space. From this point of view, a technology of precisely measuring electron density in plasma is indispensable in the design or installation stage of a plasma processing apparatus so as to identify how electron density is distributed in plasma that is created in the plasma processing space of a chamber.
Recently, for such a monitoring technology, a plasma absorption probe (PAP) method is attracting attention. This monitoring method uses an antenna probe coated with an insulation pipe, so that it does not disturb the electrical potential of plasma or does not cause metallic contamination in a chamber unlike a Langmuir probe method, thus being capable of performing measurement in the plasma of reactive gas. Furthermore, the PAP method is advantageous in that the PAP method is a measurement method in a GHz band, so that the measurement thereof is not affected by an inductive deposited film even though the inductive deposited film is attached to the surface of the insulating pipe, and thus, the PAP method can perform measurement even in the plasma of deposition gas.
As shown in FIG. 50, in the conventional PAP method (for example, refer to Patent Documents 1, 2 and 3), an insulating pipe 202 closed at the front end thereof is slidably inserted into a through hole 200a provided in the sidewall of a chamber 200, a coaxial cable 204 having a probe portion 204a formed by exposing several millimeters of the core wire of the front portion of the coaxial cable 204 is inserted into the insulating pipe 202, and the other end of the coaxial cable 204 is connected to a scalar network analyzer 206. In the chamber 200, parallel flat plate upper and lower electrodes 208 and 210 connected to, e.g., a high frequency power supply (not shown) are arranged as a plasma creating mechanism, and processing gas is supplied to a gap space between the electrodes 208 and 210 in a depressurized state, thus generating the plasma PZ of the processing gas. In the example shown, a substrate W to be processed is loaded on the lower electrode 210. An O-ring 212 for supporting the insulating pipe 202 and vacuum-sealing the through hole 200a is fitted into the through hole 200a provided in the sidewall of the chamber.
The scalar network analyzer 206 transmits a minute power electromagnetic signal (incident wave) to the probe portion 204a of the coaxial cable 204 with respect to each frequency in a band ranging from several hundred MHz to several GHz while performing frequency sweeping, such that the signal is irradiated toward the plasma PZ contained in the chamber 200, and obtains a reflection coefficient in scalar form from the ratio of the amount of power of an electromagnetic wave (reflected wave) reflected from the plasma PZ to the amount of power of the incident wave, thus obtaining the frequency characteristic of the reflection coefficient. In more detail, the probe portion 204a is placed at a desired measurement location, the high frequency power supply for plasma creation is turned off and, simultaneously, the supply of processing gas is halted, the frequency characteristic of the reflection coefficient Γ(f) (S11 parameter) is obtained by the network analyzer 206 in the state where the plasma PZ does not exist in the chamber 200, and the measured data is stored in a memory. Subsequently, by turning on the high frequency power supply and, simultaneously, supplying the processing gas, the frequency characteristic of the reflection coefficient Γ(pf) is obtained by the scalar network analyzer 206 in the state where the plasma PZ has been created in the chamber 200. Meanwhile, in the frequency characteristics of the ratio of the two reflection coefficients Γ(pf)/Γ(f), the frequency where a waveform is minimized (has the minimum peak) is considered a plasma absorption frequency. Furthermore, this plasma absorption frequency is considered to be identical with an electron frequency fp(=½π√{square root over (e2*Ne/me*ε0))} in plasma, so that electron density Ne is calculated from the following Equation 1.Ne=me*ε0*(1+εr)*(2πfp/e)2=0.012*(1+εr)*fp2[m−3]  (1)where me is an electronic mass, ε0 is a vacuum permittivity, Γr is a relative permittivity of the insulating pipe, and e is an elementary electric charge.
To investigate the spatial distribution of electron density in the plasma PZ, the probe portion 204a is sequentially moved to a plurality of measurement locations by pushing or pulling the insulating pipe 202 in the axial (longitudinal) direction, the frequency characteristics of reflection coefficients Γ(f) and Γ(pf) are obtained by the scalar network analyzer 206 while the ON and OFF of plasma creation are switched at each of the measurement locations, and the calculation of a plasma absorption frequency or electron density is performed. Generally, the location of the probe portion 204a, that is, measurement location, is moved by a desired pitch in steps, and the measured values of electron density obtained at respective measurement locations are plotted on a graph.
Furthermore, conventionally, in the development of a plasma processing apparatus, the development of a plasma process, or an actual plasma process, a technology of monitoring plasma light emission in a processing chamber has been used. In the conventional plasma light emission measuring method, plasma light emission in a chamber is measured through a window attached to the sidewall of the processing chamber. Typically, spectrum of a certain wavelength is extracted from plasma light exiting from the processing chamber through the window using a spectroscope or an optical filter, and the intensity or variation of the extracted spectrum is measured (for example, refer to Patent Document 4).
[Patent Document 1]
Japanese Unexamined Pat. Publication No. 2000-100598
[Patent Document 2]
Japanese Unexamined Pat. Publication No. 2000-100599
[Patent Document 3]
Japanese Unexamined Pat. Publication No. 2001-196199
[Patent Document 4]
Japanese Unexamined Pat. Publication No. 1998-270417